acidophiles

An acidic mud pot in Yellowstone Park – home to
the acidophile Sulfolobus acidocaldarius. Credit: US National
Park Service.

Acidophiles are microbes, including certain types of bacteria and archaea, which thrive in acidic
environments, such as sulfuric pools, where the pH values are in the range 1 to 5. They are a type of extremophile.
Because high intracellular acidity levels would destroy essential molecules,
such as DNA, acidophiles have evolved the
ability to pump hydrogen ions out of their cells at a constantly high rate.
The result is a mildly acidic internal pH of about 6.5 compared with a typical
external pH of about 2.

Several algae, such as the unicellular red
algaCyanidium caldarium and the green
algaDunaliella acidophila, are exceptional acidophiles both
of which can live below pH 1. Three fungi, Acontium cylatium, Cephalosporium sp., and Trichosporon
cerebriae, grow near pH 0. Another species, Ferroplasma acidarmanus,
has been found growing at pH 0 in acid mine drainage in Iron Mountain in
California. These polyextremophiles (tolerant to multiple environmental
extremes) thrive in a brew of sulfuric
acid and high levels of copper, arsenic, cadmium, and zinc with only a cell membrane and no cell
wall. Compare with alkaliphiles.